Semiconductor technologies have created a high demand for structuring and probing specimen in the nanometer or even in the sub-nanometer scale. Micrometer and nanometer scale process control, inspection or structuring, is often done with charged particle beams, e.g. electron beams, which are generated, deflected and focused in charged particle beam devices, such as electron microscopes or electron beam pattern generators. For inspection purposes, charged particle beams offer superior spatial resolution compared to, e.g. photon beams because their wavelengths are shorter than the wavelengths of light beams.
Inspection devices using charged particle beams such as scanning electron microscopes (SEM) have many functions in a plurality of industrial fields, including, but not limited to, inspection of electronic circuits during manufacturing, exposure systems for lithography, detecting devices, defect inspection tools, and testing systems for integrated circuits. In such particle beam systems, fine probes with high current density can be used. For instance in case of an SEM, the primary electron (PE) beam generates particles like secondary electrons (SE) and/or backscattered electrons (BSE) that can be used to image and analyze a specimen.
For high resolution imaging devices based on electron optics systems reduced aberrations and/or an improved aberration correction is one aspect to be considered. The provision of charged particle beam devices having aberration correction is beneficial. In particular, beam shaping and beam steering elements in the beam propagation path, e.g. beam deflectors, beam separators etc., may cause additional aberrations or dispersion which should be reduced or corrected in order to be able to provide for an inspection device with a high spatial resolution in the sub-nanometer range.
SEM columns are limited in their achievable resolution due to the diffraction limit, chromatic and/or spherical aberrations of the objective lens and/or other optical components included in the SEM column. In particular at low landing energies of 5 keV or below, in particular 500 eV or below, chromatic aberration is the limitation. Further, spatial dispersion of charged particles within the energy width of the charged particle beam as well as spherical aberrations may prevent a significant improvement of resolution.